1. Field of the Invention
The present invention relates to filter members for use in resin extruders (inclusive of kneaders and molding machines) and to screen changers for use in such resin extruders.
2. Discussion of the Background
A filter member for filtering off impurities contained in a resin material is incorporated in the resin passage of resin extruders (inclusive of kneaders and molding machines) adapted to extrude resin materials such as polyolefins and compounds.
A flat-type filter member is known comprising a screen for filtering off impurities and a breaker plate attached to the rear side of the screen for backing up the screen, as disclosed in Japanese Examined Patent Publication No. SHO 59-27698.
Conventional breaker plates have a multiplicity of circular resin passageways, and the ratio of opening thereof is set to about 50% to maintain a strength sufficient to back-up the screen.
For this reason, the filter member has a decreased effective filtering area within a limited area and hence tends to have a larger diameter.
It is a general practice to provide a screen between the resin melt outlet of an extruder or the like and the inlet of a mold (hereby meant to include a granulating die) to filter off impurities contained in resin melt, and to provide a device for changing the used screen soiled by much accumulation of the impurities and the like on the mesh of the screen for a new screen without the need of stopping the operation of the extruder or the like.
Conventionally known ones of this type of screen changer are described in Japanese Unexamined Patent Publication No. SHO 47-39160 and Japanese Examined Patent Publication No. SHO 59-27698. FIG. 21 shows a screen changer 60 as described in Japanese Unexamined Patent Publication No. SHO 47-39160 which includes a slide bar 65 slidably interposed between resin melt outlet 62 of an extruder 61 and inlet 64 of a molding die 63, breaker plates 67A and 67B respectively provided in a pair of resin passageways 66A and 66B extending as intersecting the moving direction of the slide bar 65, and screens 68A and 68B inserted through the breaker plates, each of the screens comprising seven bottomed cylindrical screens.
In changing the screen 68A or 68B for a new one by the screen changer 60, the slide bar 65 is made to slide so as to expose the screen 68A from between the resin melt outlet 62 of the extruder 61 and the inlet 64 of the molding die 63 and to move the other screen 68B to a position between the resin melt outlet 62 of the extruder 61 and the inlet 64 of the molding die 63, and in this condition the screen 68A is changed for a new one.
FIG. 22 shows a screen changer 70 as described in Japanese Examined Patent Publication No. SHO 59-27698 which includes a body 72 having two branched resin passages 71A and 71B and through-holes 72A and 72B extending as orthogonally crossing the resin passages 71A and 71B, respectively, slide bars 73A and 73B slidably installed in the through-holes 72A and 72B, respectively, breaker plates 75A and 75B fitted in resin passage holes 74A and 74B defined in the bars 73A and 73B, respectively, and screens 76A and 76B.
In changing the screens 76A and 76B for new ones by the screen changer 70, the slide bar 73A is made to slide so as to close the resin passage 71A and expose the screen 76A. After changing the screen 76A for a new one while allowing resin to pass through the other screen 76B, the slide bar 73A is made to slide back so as to open the resin passage 71A. Subsequently the other slide bar 73B is made to slide for the screen 76B to be changed for a new one.
With the former conventional changer 60, though the resin filtering area can be increased by increasing the number of bottomed cylindrical screens 68A and 68B, the flow of the resin melt is interrupted during the changing operation and, in addition, the screens has to be changed together with the breaker plate 67A or 67B because the number of the screens is large. Furthermore, the breaker plates 67A and 67B, if in a large plant are heavy and hot, resulting in troublesome changing operations and in difficulty in cleaning.
On the other hand, the latter conventional changer 70 has advantages that the flow of resin is never interrupted in changing the screens 76A and 76B because the resin passage is branched into two and that the changer facilitates the changing operations. Typically, the slide bars 73A and 73B are shaped like logs, and the breaker plates 75A and 75B are shaped circular for the ease of fabrication. With such circular breaker plates, if the filtering area is desired to be enlarged, the slide bars must be also enlarged in diameter, resulting in the body enlarged, hence, in the overall device enlarged. This raises critical problems in terms of space and cost.
It is, therefore, a first object of the present invention to provide a filter member having an increased effective filtering area in a limited area and hence allowing for minimization of the size thereof by forming slit-like resin passageways in a breaker plate so as to ensure an increased ratio of opening (70% to 80%) without any deterioration in the back-up capability.
It is a second object of the present invention to provide a screen changer for use in resin molding machines which permits easy screen changing operations without interrupting the flow of resin melt, facilitates cleaning operations, and provides an increased resin filtering area.
To attain the above first object, the present invention provides the following technical means in a filter member comprising in combination a screen for filtering off impurities contained in a resin material flowing in an extruder and a breaker plate having a multiplicity of resin passageways and attached to the rear side of the screen for backing up the screen.
Specifically, the present invention is characterized in that the resin passageways of the breaker plate are configured into elongated slits extending in a direction intersecting the flow direction of resin.
It is desired that the breaker plate comprise a first plate on the upstream side thereof and a second plate on the downstream side thereof which are mated to each other, the slits of one of the first and second plates being larger in width than those of the other plate and extending as intersecting those of the other plate.
Alternatively, it is desired that the breaker plate comprise a first plate on the upstream side thereof and a second plate on the downstream side thereof which are mated to each other, the resin passageways of the first plate being configured into elongated slits, and those of the second plate being configured into circular holes.
Further, the face of the breaker plate defining the resin passageways may be configured circular or rectangular, and it is desired that the screen and the breaker plate respectively comprise curved surfaces having a single curvature which protrude in the extrusion direction or the direction opposite thereto.
With the filter member according to the present invention, a resin material extruded from an extruder is filtered for its impurities by the screen of the filter member in the course of its flowing in the direction indicated by the arrow in FIG. 1(A).
Since the resin passageways of the breaker plate in the filter member are configured into elongated slits extending as intersecting the direction of the arrow, the back-up capability of the breaker plate can be sufficiently ensured even when the ratio of opening of the slits is increased relative to that of circular holes.
To attain the foregoing second object, the present invention provides the following technical means.
Specifically, the present invention provides a screen changer for use in a resin molding machine which is adapted to change a screen disposed at a resin melt outlet of an extruder or the like to filter off impurities contained in a resin melt, the screen changer comprising: an changer body in which a resin passage is divided into divided passages juxtaposed to each other in the middle of a course of the resin passage from a resin melt inlet to a resin melt outlet and in which a screen holding bar receiving bore is provided extending through the changer body as generally orthogonally intersecting each of the divided passages; a screen holding bar slidably fitted through the bore; and a screen including a bottomed cylindrical strainer and a screen mesh and mounted in one or two resin melt passage holes defined in the bar, the resin melt passage holes being capable of communicating with each of the divided passages and extending as orthogonally intersecting the axis of the bar.
In the present invention, it is desired that the screen mesh of the screen be removably attached to the strainer.
The present invention further provides a screen changer comprising: an changer body in which a resin passage is divided into divided passages juxtaposed to each other in the middle of a course of the resin passage from a resin melt inlet to a resin melt outlet and in which a screen holding bar receiving bore is provided extending through the changer body as generally orthogonally intersecting each of the divided passages; a screen holding bar slidably fitted through the bore; a screen changeably mounted in one or two resin melt passage holes defined in the bar, the resin melt passage holes being capable of communicating with each of the divided passages and extending as orthogonally intersecting the axis of the bar; and a breaker plate having a multiplicity of through holes and attached to the resin flow-out side of the screen, wherein each of the resin melt passage holes are configured square in section at least on the resin flow-in side thereof, and the screen and the breaker plate, which are configured square, are disposed on the resin flow-in side of each of the resin melt passage holes.
It is desired that the breaker plate or each of the resin melt passage holes of the screen holding bar be provided therein with a scaling wall.
With the screen changer according to the present invention, resin melt introduced in the changer from the outlet of an extruder cc the like passes through each of the divided passages, is filtered with the respective screen mesh, join together, and is guided to a mold or the like. In changing the screens, one of die screen holding bars is slid to expose the corresponding screen while, at the same time, one of the divided passages is closed by the screen holding bar. Then, only the soiled screen mesh of the exposed screen is changed for a new one while the resin melt is allowed to pass through the other screen. The screen holding bar then is slid in the opposite direction to return the new screen into the divided passage.
In turn, the other screen holding bar is slid to expose the screen thereof and to close the other divided passage. The soiled screen mesh of the thus exposed screen is changed for a new one while the resin melt is allowed to pass through the other screen previously changed. Subsequently the screen holding bar of interest is slid in the opposite direction to return the screen thereof into the divided passage to permit resin melt to pass therethrough.
As obvious from FIG. 15, by configuring the breaker plate into square it is possible to ensure a larger filtering area than conventional without varying the diameter of the screen holding bar. This allows for large-capacity filtration thereby enabling the production to increase.
Further, the provision of a sealing wall in the breaker plate or in each of the resin passage holes along with the breaker plate in square configuration prevents resin melt from flowing out of the screen changer and makes it possible to shorten a sealing portion between the changer body and the screen holding bars, thereby reducing the size of the changer body, assuring the screen changer worked with improved precision, and reducing the working cost.